1. Field of the Invention
This invention relates to process for producing methacrolein in a high yield by oxidizing isobutylene or tertiary butanol with molecular oxygen with a specific catalyst.
2. Description of the Prior Art
Hitherto, many catalysts have been proposed for the gas phase catalytic oxidation of isobutylene or tertiary butanol. From the industrial point of view, however, there are yet many points to be improved.
For example, in the production of methacrolein, the yield of the product, methacrolein, based on the starting material (isobutylene or tertiary butanol) is still so low that the selectivity based on isobutylene is at most about 82-86% even with a catalyst which has hitherto been called an excellent catalyst. Therefore, a catalyst system capable of giving a much higher selectivity is desired. Some of the catalysts containing molybdenum as a main component and additionally containing tellurium exhibit a considerably high yield in the early stage of the reaction. However, their activities drop markedly owing to structural change and scattering of tellurium, and there has been found substantially no catalyst enabling methacrolein to be obtained in a high yield for a long period of time.
When it is intended to use the resulting methacrolein as a starting material for producing an unsaturated ester directly from an unsaturated aldehyde, it is desired that the amount of by-products such as methacrylic acid and acetic acid is as small as possible. Thus, the use as an industrial catalyst involves a number of problems. The present inventors have conducted earnest and detailed studies with the aim of solving the above-mentioned problems. As a result, this invention has been accomplished.